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The structures and energetics of species with the stoichiometries (Me2CNO)M(CO)nCp (M = Cr, Mo, W; n = 3, 2, 1; Cp = η5-C5H5) have been studied by density functional theory. The experimental structure Mo2-1S with an NO-dihapto Me2CNO ligand found by X-ray crystallography for (Me2CNO)Mo(CO)2Cp is shown to be the lowest energy isomer by a substantial margin. The expected initial Me2CNOMo(CO)3Cp product from the reaction of NaMo(CO)3Cp with Me2C(NO)Br used to synthesize (Me2CNO)Mo(CO)2Cp is predicted to undergo facile CO dissociation based on ΔH and ΔG values. The energetics of the currently unknown analogous chromium and tungsten systems appear to be similar to that of the molybdenum system. The structures Me2NC(CO)OM(CO)2Cp (M = Cr, Mo, W) with a dimethylcarbamate ligand are much lower energy (Me2CNO)M(CO)3Cp isomers but are clearly not accessible from reactions of the anions CpM(CO)3− with Me2C(NO)Br. The lowest energy structures for the monocarbonyl (Me2CNO)M(CO)Cp are of the type (Me2C＝N)M(O)(CO)Cp with separate dimethylimino and oxo ligands formed by oxidative addition of the Me2CNO unit to the central metal atom. [ABSTRACT FROM AUTHOR]

The first‐row transition metal 1‐norbornyl derivatives CpM(nor) Cp = η5‐C5H5; nor = 1‐norbornyl; M = Ti to Cu), including the experimentally known CpNi(nor) reported by Lehmkuhl and Dimitrov, have been examined by density functional theory and benchmarked by the more accurate DLPNO‐CCSD(T) method. The lowest energy CpM(nor) structures for the later first row transition metals from manganese to copper are found to be high‐spin state structures in which the 1‐norbornyl ligand is bonded to the metal only through the M–C σ‐bond to the bridgehead carbon atom. The favored spin states range from doublet for CpCu(nor) to sextet for CpMn(nor). The pattern of favorable structure types changes for the CpM(nor) derivatives of the earlier first row transition metals to the left of manganese since all of their low energy structures have singly or doubly agostic 1‐norbornyl groups. The agostic C–H–M interactions in the CpM(nor) derivatives are characterized by their reduced density gradients and low ν(C–H) frequencies. [ABSTRACT FROM AUTHOR]

Structures of the slightly hypoelectronic 14-vertex species Cp2M2B12H12 (M = Rh, Ir) and Cp2M′2C2B10H12 (M′ = Ru, Os) with 28 Wadean skeletal electrons, including the experimentally known Cp*2Ru2C2B10H12, have been optimized by density functional theory. All low-energy such structures have the metal atoms located at degree 6 vertices. The lowest energy structures have central M2B12 and M′2C2B10 deltahedra with three degree 6 vertices, one degree 4 vertex, ten degree 5 vertices, and the metal atoms located at non-adjacent non-antipodal degree 6 vertices similar to meta isomers of icosahedral dimetallaboranes. Slightly higher energy structures are based on the same central deltahedron but with the metal atoms located at adjacent degree 6 vertices similar to ortho isomers of dimetallaboranes. Isomeric structures with central M2B12 and M′2C2B10 central closo deltahedra, namely bicapped hexagonal antiprisms with the metal atoms in antipodal positions at the two degree 6 vertices similar to the para isomers of icosahedral dimetallaboranes, also lie at low energies. [ABSTRACT FROM AUTHOR]

The structures and energetics of the bis(butadiene) complexes of the second row transition metals (C4H6)2M) M=Zr to Pd) have been investigated by density functional theory. The energetically accessible (C4H6)2M structures (M=Zr to Rh) are found to have only tetrahapto η4‐C4H6 ligands. The second row transition metals energetically prefer low spin states in their bis(butadiene) derivatives (C4H6)2M reflecting their increased ligand field strength relative to the first row transition metals. Thus the energies of the singlet and doublet spin states for (C4H6)2Ru and (C4H6)2Tc, respectively, are lower than their triplet and quartet spin state isomers in contrast to the corresponding iron and manganese systems, respectively. Furthermore, the staggered maximum spin (C4H6)2M structures with χ ≈ 90° having tetrahedral coordination of the central metal to the four C=C double bonds of the two butadiene ligands found as lowest energy structures for the first row transition metals are not found for the second row transition metals from Mo to Pd. Instead the lowest energy (C4H6)2M structures for the second row transition metals have an eclipsed confirmation with χ ≈ 0° implying square planar coordination of the central metal. The lowest energy structure of the palladium complex (C4H6)2Pd is anomalous since only one of the two butadienes is a tetrahapto ligand whereas the second butadiene is only a dihapto ligand leaving one uncomplexed C=C double bond. [ABSTRACT FROM AUTHOR]

The 1-norbornyl (nor) ligand is known experimentally to form stable transition metal alkyl derivatives through direct metal–carbon bond formation. This appears to be related to its steric bulk and inaccessibility towards β-hydrogen elimination, as exemplified by the tetraalkyls (nor)4M, some of which are very stable. In this connection we have used density functional theory and the DLPNO-CCSD(T) method to investigate the 1-norbornylcobalt carbonyl derivatives (nor)Co(CO)n (n = 4, 3, 2, 1) and (nor)2Co2(CO)n (n = 7, 6, 5). Low-energy structures of the unsaturated systems (nor)Co(CO)n (n = 3, 2) and (nor)2Co2(CO)n (n = 6, 5) are found to have agostic hydrogen atoms from a CH2 group adjacent to the Co–C bond. Such agostic hydrogen atoms form a C–H–Co bridge with a bonding Co–H distance less than ∼2 Å. In such structures unsaturation is relieved by donation of an additional two electrons from the C–H bond of this norbornyl CH2 group. In addition, structures in which carbonyl migration from cobalt to carbon has occurred to form acyl norCO ligands are among the lowest energy structures. The resulting acyl carbonyl groups of the norCO ligands serve as spacers between the bulky 1-norbornyl ligand and the cobalt carbonyl moiety. Furthermore, such neutral norCO acyl ligands can either be one-electron donors to a cobalt atom, bonding solely through the carbonyl carbon, or three-electron donor η2-μ-norCO groups bridging a central Co2 unit through both the acyl carbon and oxygen atoms. The strengths of the agostic C–H–Co interactions have been characterized by their reduced density gradient (RDG) values. [ABSTRACT FROM AUTHOR]

The geometries and energetics of the bis(bicyclo[3.2.1]octa-2,6-dien-4-yl) complexes of the first row transition metals, (bcod)2M (M = Ti to Cu), including the experimentally known chromium and iron derivatives, have been examined by density functional theory. Sandwich-type structures in which each bcod ligand is bonded to the central metal atom through both the trihapto allylic unit and the double bond are energetically preferred for the metals from titanium to iron. However, higher energy (bcod)2M (M = V, Cr, Mn) isomers are found in which one of the bcod ligands is bonded to the central metal atom through the trihapto allylic unit and an agostic hydrogen from the CH2 bridge leaving an uncomplexed C＝C double bond. The experimentally known iron complex (bcod)2Fe, an analogue of ferrocene, has the favored 18-electron configuration and a singlet spin state. For the metals to the left of iron from manganese to vanadium the energetically preferred spin states range from doublet to quartet, respectively, corresponding to holes in the closed shell 18-electron configuration. However, a singlet structure is preferred for (bcod)2Ti despite the 14-electron configuration of the central titanium atom. The (bcod)2M (M = Co, Ni, Cu) derivatives of the electron richer later transition metals are characterized by several structures of different types at closely spaced energies in which at least one of the bcod ligands is only partially bonded to the central metal atom. [ABSTRACT FROM AUTHOR]

The experimentally known cobalt ethylenedithiolate complex CpCoS2C2H2 as well as its rhodium and iridium analogues are aromatic systems that can function as pentahapto six-electron donor metallodithiolene ligands by binding through all five atoms of its CoS2C2 ring. The lowest energy CpMS2C2H2·Cr(CO)n (n = 3, 2) and CpMS2C2H2·Fe(CO)2 structures (M = Co, Rh, Ir) by substantial margins are predicted by density functional theory to have structures with such pentahapto η5-(CpMS2C2H2) (M = Co, Rh, Ir) ligands. The CpMS2C2H2·Cr(CO)3 structures appear to be favorable as indicated by high carbonyl dissociation free energies (ΔG) exceeding 15 kcal mol−1. The lowest energy structures for the carbonyl-richer CpMS2C2H2·Cr(CO)4 and CpMS2C2H2·Fe(CO)3 systems have trihapto CpMS2C2H2 ligands involving a heterometallic metal–metal bond and two metal–sulfur bonds retaining an uncomplexed C＝C double bond in the ethylenedithiolate ligands. The CpMS2C2H2·Fe(CO)3 structures can be derived from the structures of the long-known (RS)2Fe2(CO)6 derivatives by replacing one of the Fe(CO)3 units by an isoelectronic/isolobal CpM unit. Such CpMS2C2H2·Fe(CO)3 structures appear to be favorable as indicated by high carbonyl dissociation free energies (ΔG) exceeding 15 kcal mol−1. Higher energy CpMS2C2H2·Cr(CO)4 and CpMS2C2H2·Fe(CO)3 structures involve coordination of the C＝C double bond and at least one sulfur atom of the CpMS2C2H2 ligand to the chromium or iron atom but have long metal–metal distances suggesting lack of a direct heterometallic metal–metal bond. In the lowest energy structures of the still carbonyl richer CpMS2C2H2·Cr(CO)5 and CpMS2C2H2·Fe(CO)4 the CpMS2C2H2 ligand is a dihapto ligand that is bonded to the chromium or iron atom through a heterometallic M–M′ (M′ = Cr, Fe) bond and a metal–sulfur bond. Other types of dihapto ligand–metal bonding found in higher energy CpMS2C2H2·Cr(CO)5 and CpMS2C2H2·Fe(CO)4 structures include bonding only the C＝C double bond of the ethylenedithiolate ligand to the chromium or iron atom as in a simple (olefin)M(CO)n complex or bonding of adjacent carbon and sulfur atoms in the CpMS2C2H2 ligand to the chromium or iron atom. The latter mode of dihapto C,S bonding of the CpMS2C2H2 ligand can be interpreted as a π-bond from a C＝S double bond in the dithioglyoxal structure for CpMS2C2H2. [ABSTRACT FROM AUTHOR]

The geometries and energetics of the binuclear fluoroborylene manganese carbonyls Mn2(BF)2(CO)n (n = 8, 7, 6) have been investigated using density functional theory. Coupling of two fluoroborylene ligands to give a bridging difluorodiborene μ-B2F2 ligand with a relatively long ∼1.9 Å B–B bond has been observed in two of the three lowest energy Mn2(BF)2(CO)7 structures as well as the lowest energy Mn2(BF)2(CO)6 structure. Higher energy Mn2(BF)2(CO)6 structures have two separate bridging BF groups and short Mn≡Mn distances of ∼2.3 Å suggesting the formal triple bond required by the 18-electron rule. [ABSTRACT FROM AUTHOR]

Density functional theory studies show that the lowest energy C4F8Fe(CO)4 structure is not the very stable experimentally known ferracyclopentane isomer (CF2CF2CF2CF2)Fe(CO)4 obtained from Fe(CO)12 and tetrafluoroethylene. Instead isomeric (perfluoroolefin)Fe(CO)4 structures derived from perfluoro-2-butene, perfluoro-1-butene, and perfluoro-2-methylpropene are significantly lower energy structures by up to ∼17 kcal mol−1. However, the activation energies for the required fluorine shifts from one carbon to an adjacent carbon atom to form these (perfluoroolefin)Fe(CO)4 complexes from tetrafluoroethylene are very high (e.g., ∼70 kcal mol−1). Therefore the ferracyclopentane isomer (CF2CF2CF2CF2)Fe(CO)4, which does not require a fluorine shift to form from Fe3(CO)12 and tetrafluoroethylene, is the kinetically favored product. The lowest energy structures of the binuclear (C4F8)2Fe2(CO)n (n = 7, 6) derivatives have bridging perfluorocarbene ligands and terminal perfluoroolefin ligands. [ABSTRACT FROM AUTHOR]

The known sandwich compound [η5-(CH2)3N2(BPh)2CMe]2Fe in which adjacent C2 units are replaced by isoelectronic BN units can be considered as a boraza analogues of ferrocene similar to borazine, B3N3H6, considered as a boraza analogue of benzene. In this connection, the related bis(1,2,3,5-tetramethyl-1,2-diaza-3,5-diborolyl) derivatives (Me4B2N2CH)2M (M = Ti, V, Cr, Mn, Fe, Co, Ni) for all of the first row transition metals have been optimized using density functional theory for comparison with the isoelectronic tetramethylcyclopentadienyl derivatives (Me4C5H)2M. Low-energy sandwich structures having parallel B2N2C rings in a trans orientation are found for all seven metals. The 1,2-diaza-3,5-diborolyl ligand appears to be a weaker field ligand than the isoelectronic cyclopentadienyl ligand as indicated by higher spin ground states for some (η5-Me4B2N2CH)2M sandwich compounds relative to the corresponding metallocenes (η5-Me4C5H)2M. Thus (η5-Me4B2N2CH)2Cr has a quintet ground state in contrast to the triplet ground state of (η5-Me4C5H)2Cr. Similarly, the sextet ground state of (η5-Me4B2N2CH)2Mn lies ∼18 kcal mol−1 below the quartet state in contrast to the doublet ground state of the isoelectronic (Me4C5H)2Mn. These sandwich compounds are potentially accessible by reaction of 1,2-diaza-3,5-diborolide anions with metal halides analogous to the synthesis of [η5-(CH2)3N2(BPh)2CMe]2Fe. [ABSTRACT FROM AUTHOR]

Doped clusters by Si16 cage encapsulating group‐IV metal atoms (M@Si16, M = Ti, Zr and Hf) are computationally investigated by both density functional theory (DFT) and high‐level CCSD(T) method. Their low‐energy structures are globally searched using a genetic algorithm based on DFT. The ground state structures of neutral and anionic M@Si16 are determined by calculating the vertical and adiabatic detachment energies and comparing them with the experimental data. For neutral Ti@Si16, the Frank‐Kasper (FK) deltahedron with Td symmetry and distorted FK isomer with C3v symmetry are nearly degenerate as the ground state and may coexist in laboratory, while the distorted FK isomer is the most probable structure for Ti@Si16− anion. For neutral and anionic Zr@Si16 and Hf@Si16 clusters, the ground states at finite temperatures up to 300 K are the fullerene‐like D4d bitruncated square trapezohedron. These theoretical results establish a more complete picture for the most stable structures of M@Si16 clusters, which possess large gaps and may serve as building blocks for electronic and optoelectronic applications. By comparing the simulated photoelectron spectra with the experimental data, the ground states of the M@Si16 (M = Ti, Zr, and Hf) clusters were identified. The FK1 isomer is the most probable ground state for the Ti@Si16− anion, and the f isomer is always the lowest‐energy state at temperatures up to 300 K for Zr@Si16 and Hf@Si16 clusters. [ABSTRACT FROM AUTHOR]

The skeletal bonding topology as well as the Re=Re distances and Wiberg bond indices in the experimentally known oblatocloso dirhenaboranes Cp*2Re2Bn-2Hn-2 (Cp*=η5Me5C5, n=8-12) suggest formal Re=Re double bonds through the center of a flattened Re2Bn-2 deltahedron. Removal of a boron vertex from these oblatocloso structures leads to oblatonido structures such as Cp2W2B5H9 and Cp2W2B6H10. Similar removal of two boron vertices from the Cp2Re2Bn-2Hn-2 (n=8-12) structures generates oblatoarachno structures such as Cp2Re2B4H8 and Cp2Re2B7H11. Higher energy Cp2Re2Bn-2Hn-2 (Cp=η5-C5H5, n=8-12) structures exhibit closo deltahedral structures similar to the deltahedral borane dianions BnHn2-. The rhenium atoms in these structures are located at adjacent vertices with ultrashort Re≣Re distances similar to the formal quadruple bond found in Re2Cl82- by X-ray crystallography. Such surface Re≣Re quadruple bonds are found in the lowest energy PnRe2Bn-2Hn-2 structures (Pn=η5,η5-pentalene) in which the pentalene ligand forces the rhenium atoms to occupy adjacent deltahedral vertices. The low-energy structures of the tritungstaboranes Cp3W3(H)Bn-3Hn-3 (n=5-12), related to the experimentally known Cp*3W3(H)B8H8, have central W3Bn-3 deltahedra with imbedded bonded W3 triangles. Similar structures are found for the isoelectronic trirhenaboranes Cp3Re3Bn-3Hn-3. The metal atoms are located at degree 6 and 7 vertices in regions of relatively low surface curvature whereas the boron atoms are located at degree 3-5 vertices in regions of relatively high surface curvature. The five lowest-energy structures for the 11-vertex tritungstaborane Cp3W3(H)B8H8 all have the same central W3B8 deltahedron and differ only by the location of the "extra" hydrogen atom. The isosceles W3 triangles in these sW-W edge of ~2.7 to ~2.8 Å corresponding to a surface deltahedral edge. [ABSTRACT FROM AUTHOR]

The geometries and energetics of tritungstaboranes Cp3W3(H)Bn−3Hn−3 (Cp = η5-C5H5; n = 5 to 12), related to the experimentally known Cp*3W3(H)B8H8 (Cp* = η5-Me5C5), have been investigated using density functional theory and coupled cluster calculations. Such low-energy structures have central W3Bn−3 deltahedra with superimposed bonded W3 triangles. The “extra” hydrogen atom either bridges a deltahedral edge or caps a deltahedral face containing at least one tungsten atom. The tungsten atoms are located at degree 5 to 7 vertices in regions of a relatively low surface curvature whereas the boron atoms are located at degree 3 to 5 vertices in regions of a relatively high surface curvature. The five lowest-energy structures of the 11-vertex tritungstaborane Cp3W3(H)B8H8 all have the same central W3B8 deltahedron and differ only by the location of the “extra” hydrogen atom. The isosceles W3 triangles in these structures have two long ∼3.0 Å W–W edges through the inside of the deltahedron with the third shorter W–W edge of ∼2.7 to ∼2.8 Å corresponding to a surface deltahedral edge. The five Cp3W3(H)B8H8 structures differ only by the location of the “extra” hydrogen atom. The lowest energy such structure has the “extra” hydrogen atom bridging the surface W–W bond and corresponds to the experimental Cp*3W3(H)B8H8 structure, as determined using X-ray crystallography. [ABSTRACT FROM AUTHOR]

Experimentally characterized endohedral metallofullerenes are of current interest in expanding the range of viable fullerenic structures and their applications. Smaller metallofullerenes, such as M@C28, show that several d- and f-block elements can be efficiently confined in relatively small carbon cages. This article explores the potential capabilities of the smallest fullerene cage, that is, C20, to encapsulate p-block elements from group 14, that is, E = Si, Ge, Sn, and Pb. Our interest relates to the bonding features and optical properties related to E@C20. The results indicate both s- and p-type concentric bonds, in contrast to the well explored endohedral structures encapsulating f-block elements. Our results suggest the E@C20 series to be a new family of viable endohedral fullerenes. In addition spectroscopic properties related to electron affinity, optical, and vibrational were modeled to gain further information useful for characterization. Characteristic optical patterns were studied predicting a distinctive first peak located between 400 and 250 nm, which is red-shifted going to the heavier encapsulated Group 14 atoms. Electron affinity properties expose different patterns useful to differentiate the hollow C20 fullerene to the proposed p-block endohedral counterparts. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The unexpected 2004 discovery of decamethyldizincocene suggested some new possibilities for organometallic compounds in which an M2 unit is sandwiched between two planar carbocyclic rings. Density functional theory shows that the low-energy structures for the dizincocenes Zn2(C5X5)2 (X = H, F) are singlet coaxial structures having two (η5-C5X5)Zn units linked by a Zn–Zn single bond of length ∼2.3 Å. However, the low-energy M2(C5H5)2 (M = Cu, Ni, Co, Fe) structures have perpendicular configurations with bridging C5H5 ligands. They exhibit increasingly higher spin states from singlet (Cu, Ni) to triplet (Ni,Co), quintet (Co,Fe), and septet (Fe). The low-energy structures of the perfluorinated systems M2(C5F5)2 (M = Co, Fe) have irregular geometries with one bent bridging C5F5 ring and one planar terminal pentahapto η5-C5F5 ring, with the metal atom bearing the terminal η5-C5F5 ligand has the favored 18-electron configuration while the other metal atom has only a lower electron configuration and vacant coordination sites. [ABSTRACT FROM AUTHOR]

Density functional theory has been used to examine the dimetallocene-like dicycloheptatrienyl dimetal compounds of the second-row transition metals (C7H7)2M2 (M5Ru, Tc, Mo, Nb, Zr). The lowest energy (C7H7)2Mo2 structure is a coaxial structure with terminal η7-C7H7 rings, whereas the lowest energy (C7H7)2M2 structures (M5Ru, Tc, Nb, Zr) are perpendicular structures with bridging η4,η4-7H7 rings except for the perpendicular (η4,η3-C7H7)2Ru2 structure. The metal- metal bond orders in the (C7H7)2M2 structures (M5Ru, Tc, Mo, Nb), as determined by analysis of their frontier molecular orbitals, suggest preferred 16- rather than 18-electron configurations for the central metal atoms. Thus, in the coaxial (57-C7H7)2M2 structures the formal bond orders are two for M = Tc and three for M = Mo. For the perpendicular structures both (η4,η3-C7H7)2Ru2 and (η4,η4-C7H7)2Tc2 have 16-electron configurations with metal-metal single bonds owing to the different modes of bonding of the bridging C7H7 rings in the two structures. For the (C7H7)2Zr2 system the perpendicular structure has a formal Zr=Zr double bond and the coaxial structure has a very long (~3.5 Å) Zr-Zr bond indicating only 12- to 14-electron configurations for the zirconium atoms. [ABSTRACT FROM AUTHOR]

Binuclear chromium carbonyl complexes of the general type [MeN(PF2)2]mCr2(CO)n, including the experimentally known [MeN(PF2)2]3Cr2(CO)n (n = 6, 5) species, have been studied by density functional theory (DFT) methods. The lowest energy structures for the three series of [MeN(PF2)2]mCr2(CO)n (m = 1, 2, 3) structures can be grouped into three triads, namely [MeN(PF2)2]Cr2(CO)n (n = 10, 9, 8), [MeN(PF2)2]2Cr2(CO)n (n = 8, 7, 6), and [MeN(PF2)2]3Cr2(CO)n (n = 6, 5, 4). The carbonyl richest structures of each triad, namely [MeN(PF2)2]Cr2(CO)10, [MeN(PF2)2]2Cr2(CO)8, and [MeN(PF2)2]3Cr2(CO)6 have all terminal carbonyl groups, no chromium–chromium bond, and the MeN(PF2)2 ligands bridging the pair of chromium atoms. However, for [MeN(PF2)2]3Cr2(CO)6 a structure with two of the three MeN(PF2)2 ligands chelating to single chromium atoms are energetically competitive. Low-energy singlet spin state structures for the intermediate and carbonyl poorest members of each triad can incorporate a variety of features such as chromium–chromium single and double bonds, MeN(PF2)2 ligands split into bridging MeNPF2 + PF2 groups, and four-electron donor bridging η2-μ-CO groups as required to give each chromium atom the favored 18-electron configuration. Such four-electron donor bridging η2-μ-CO groups are not found in low-energy structures of related binuclear carbonyl complexes [MeN(PF2)2]mM2(CO)n (M = Fe, Ni; m = 1, 2) of the later transition metals iron and nickel. [ABSTRACT FROM AUTHOR]

The experimentally characterized endohedral metallic fullerenes involving the small C28 cage, has shown to be able to encapsulate zirconium, hafnium, and uranium atoms, among other elements. Here, we explore the formation and nature of concentric bonds from purely d- to f-block elements, given by Zr, Hf, and uranium, along a borderline metal between such blocks, thorium. We explore the interplay of d- and f-orbitals in the chemistry of the early actinides, where the features of a d- or f-block metal can be mixed. Our results indicate that the bonding of Th@C28 involves contributions from both d- and f-type bonds, as characteristic of this early actinide element. Even uranium in U@C28, also exhibits a contribution from d-type bonds in addition to its relevant f-block character. Electron affinity and optical properties were evaluated to gain more insights into the variation of these molecular properties in this small endohedral fullerene, along Zr, Hf, Th, and U. The current results, allows to unravel the role of ( n − 1)d and ( n − 2)f orbitals in confined elements ranging from d- to f-blocks, which can be useful to gain a deeper understanding of the bonding situation in other endohedral species. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A density functional theory study of experimentally reported [M](C3E2) complexes ([M] = Ir, Ni, Pt surrounded by ligands such as phosphines and halides; E = O, S, Se) suggests that the behaviors of C3O2 and C3E2 (E = S, Se) as ligands in transition metal complexes differ significantly. The lowest energy structures for the [M](C3O2) complexes have the C3O2 ligand bonded to the transition metal through a C=C double bond. However, the lowest energy structures for the [M](C3E2) (E = S, Se) complexes have the C3E2 ligand bonded to the transition metal through a C=E double bond. The latter structures are confirmed by comparison of the experimental infrared frequencies arising from the C3E2 ligand with our theoretical results. [ABSTRACT FROM AUTHOR]

The structures and energetics of the acenaphthylene iron carbonyl complexes (C12H8)Fe(CO)n (n = 4, 3, 2), (C12H8)Fe2(CO)n (n = 8, 7, 6, 5, 4), and (C12H8)Fe3(CO)n (n = 9, 8), including the known (η2-C12H8)Fe(CO)4 and (η5,η3-C12H8)Fe2(CO)5, have been examined using density functional theory. The two experimentally known (η5,η3-C12H8)Fe2(CO)5 structures, related by a thermally reversible photochemical haptotropic rearrangement, lie within ∼1 kcal mol−1 from each other in energy and more than 20 kcal mol−1 below any other (C12H8)Fe2(CO)5 isomers. Decarbonylation of the pentacarbonyl to the tetracarbonyl (C12H8)Fe2(CO)4 is predicted to retain the formal Fe–Fe single bond but to convert one of the CO groups to a four-electron donor bridging η2-μ-CO group. The lowest-energy carbonyl-rich (C12H8)Fe2(CO)n (n = 8, 7, 6) structures lack direct iron–iron bonds and have the ligand hapticities expected from the 18-electron rule. The low CO dissociation energy of ∼5 kcal mol−1 for (C12H8)Fe2(CO)6 suggests that these carbonyl-rich species are not viable. The addition of an Fe(CO)3 moiety to the binuclear (C12H8)Fe2(CO)n (n = 6, 5) complexes to give the trinuclear (C12H8)Fe3(CO)n (n = 9, 8) complexes, respectively, is predicted to be exothermic by ∼50 kcal mol−1. These trinuclear complexes have pentahapto–bis(trihapto) acenaphthylene ligands with an Fe–Fe bond in the octacarbonyl structures. The experimental mononuclear (η2-C12H8)Fe(CO)4 structure with a dihapto acenaphthylene ligand is the lowest energy isomer. The hapticity of the acenaphthylene ligand increases from dihapto to pentahapto or hexahapto upon CO loss to give (C12H8)Fe(CO)n (n = 3, 2). [ABSTRACT FROM AUTHOR]

The experimentally synthesized and structurally characterized metallaborane clusters containing highly electronegative heteroatoms namely (S, P, and Se) were studies by density functional theory in order to provide an insight into the influence of these heteroatoms on the polyhedral framework of metallaboranes. [ABSTRACT FROM AUTHOR]

The geometries and energetics of the trirhenaboranes Cp3Re3Bn−3Hn−3 (Cp = η5-C5H5; n = 5 to 12) have been investigated using density functional theory for comparison with the experimentally known oblatocloso dirhenaboranes Cp*2Re2Bn−2Hn−2 (Cp* = η5-Me5C5; n = 8 to 12). The low-energy Cp3Re3Bn−3Hn−3 (7 ≤n≤ 12) structures are found to be Re3Bn−3 deltahedra with internally bonded Re3 triangles. The rhenium atoms are generally located at degree 6 to 8 vertices representing sites of low local curvature and the boron atoms at degree 3 to 5 vertices representing sites of high local curvature. The Re–Re bonds in the Re3 triangles of such clusters typically range from 2.6 to 2.7 Å if they are located on or near the deltahedral surface and from 2.8 to 3.0 Å if they go through the interior of the deltahedron away from the surface. Such highly non-spherical structures, typically having little symmetry, are related to the oblatocloso structures of the dirhenaboranes. A low-energy, more nearly spherical 12-vertex Cp3Re3B9H9 structure, essentially degenerate with the global minimum, has an Re–Re–Re chain embedded in a deltahedron having degree 5 and 6 rhenium vertices and degree 4 and 5 boron vertices. Low-energy structures for the 5-vertex Cp3Re3B2H2 system are derived from a trigonal bipyramid. Similarly, low-energy 6-vertex Cp3Re3B3H3 structures have central Re3B3 bicapped tetrahedra. [ABSTRACT FROM AUTHOR]

The experimentally known CpFeMn(CO)7 system as well as the related unsaturated CpFeMn(CO)n systems (n = 6, 5) have been investigated by density functional theory. For CpFeMn(CO)7 unbridged and doubly bridged structures with a heteronuclear Fe–Mn single bond lie within ∼5 kcal mol−1 of each other with the experimentally known unbridged structure being the lower energy structure. The three lowest-energy unsaturated CpFeMn(CO)6 structures, lying within ∼1 kcal mol−1 of each other, have very diverse structural features. The lowest-energy CpFeMn(CO)6 structure contains an unusual three-center two-electron C–H–Mn bond involving an agostic hydrogen of the Cp ring. Another such structure is a triply bridged triplet CpFe(μ-CO)3Mn(CO)3 closely related to the experimentally known Cp2Fe2(μ-CO)3 having a central UGRAPHIC DISPLAY="INLINE" ID="UGT2" SRC="UGT2"/ Fe=Mn double bond containing the two unpaired electrons of the triplet spin state. The third low-energy CpFeMn(CO)6 structure is a CpFe(CO)Mn(CO)4(η2-μ-CO) structure with a four-electron donor bridging η2-μ-CO group similar to that found in the lowest energy Mn2(CO)9 structure. The lowest-energy structure of the even more unsaturated CpFeMn(CO)5 has a short Fe≡Mn distance of only ∼2.2 Å suggesting a formal triple bond. Higher energy CpFeMn(CO)5 structures have a four-electron donor η2-μ-CO group in addition to a formal Fe=Mn double bond. The CpFeMn(CO)5 structure in which the oxygen atom of the η2-μ-CO group is bonded to manganese lies ∼9 kcal mol−1 in energy below the isomeric structure in which the oxygen of the η2-μ-CO group is bonded to iron. [ABSTRACT FROM AUTHOR]

Uhl and coworkers have synthesized and characterized structurally the 11-vertex tetracarbalanes (AlMe)7(CEt)4(μ-H)2 and (AlEt)7(CCH2Ph)4(C≡CPh)(μ–H). In order to understand the nature of the unusual C4Al7 polyhedra in such systems, the complete series of permethylated tetracarbalanes C4Aln−4Men (n = 6 to 14) as model compounds have been investigated using density functional theory. An overriding factor in determining the polyhedra for the lowest energy structures of a wide range of tetracarbalanes C4Aln−4Men (n = 6 to 14) is the availability of vertices of degrees 3 and 4 for all four carbon atoms. For the 11-vertex C4Al7Me11 system the experimentally observed C4Al7 deltahedron with carbon atoms at the four degree 4 vertices is found in the lowest energy structure but severely distorted from ideal C2h to Cs symmetry. This distortion is removed by adding two bridging hydrogens to the C4Al7Me11 structure in the same locations as in the experimental structures. The lowest energy structures of the tetracarbalanes C4Aln−4Men (n = 12, 13, 14) with more than 11 vertices are deltahedra having the carbon atoms at degree 4 vertices similar to the lowest energy C4Al7Me11 structures. The lowest energy structures for the smaller tetracarbalanes C4Aln−4Men (n = 6, 7, 8) are nido structures with pentagonal or hexagonal open faces related to nido borane structures. The intermediate 9- and 10-vertex tetracarbalanes C4Aln−4Men (n = 9, 10) have relatively complicated energy surfaces. [ABSTRACT FROM AUTHOR]

The structures and energetics of the complete series of hydrogen-rich dimetallaboranes Cp2M2B6H10 and Cp*2M2B6H10 (Cp = η5-C5H5; Cp* = η5-Me5C5; M = Pd, Pt; Rh, Ir; Ru, Os; Re; Mo, W; Ta), including the experimentally known Cp*2Rh2B6H10 and Cp*2W2B6H10 (Cp* = η5-Me5C5), have been investigated by density functional theory. The lowest energy structures of the hyperelectronic Cp2M2B6H10 (M = Pd, Pt; Rh, Ir) systems have central M2B6 frameworks with a hexagonal open face similar to the B8 networks in arachno-B8H14 and nido-B8H12. The two lowest energy structures for Cp2Rh2B6H10 and Cp*2Rh2B6H10, lying within 1 kcal mol−1 of energy, differ only in the locations of the bridging hydrogen atoms around the hexagonal hole consistent with the experimentally observed fluxionality of the hydrogen atoms in Cp*2Rh2B6H10. Most of the lowest energy Cp2M2B6H10 (M = Ru, Os) structures also have a central M2B6 framework similar to B8H12, typically with such additional features as an additional metal–metal bond or a formal metal–metal double bond. A common motif for the low-energy structures of the hypoelectronic Cp2M2B6H10 (M = Re; Mo, W; Ta) systems, including the experimentally known Cp*2W2B6H10, is a central M2B4 octahedron with its two M2B faces capped by the remaining boron atoms and with four M–B edges bridged by hydrogen atoms. Such structures can also be considered as oblatonido structures derived from the experimentally known 9-vertex oblatocloso Cp*2Re2B7H7 structure by removal of the unique degree 4 vertex atom. [ABSTRACT FROM AUTHOR]

Reactions of cyclooctatetraene with iron carbonyls under various conditions give not only the monomeric (η4-C8H8)Fe(CO)3 but three C8H8Fe2(CO)6 isomers and one C8H8Fe2(CO)5 isomer. Density functional theory on the C8H8Fe2(CO)6 system shows the trans-(η4,η4-C8H8)Fe2(CO)6 isomer to be the lowest energy isomer. The cis-(η3,η3-C8H8)Fe2(CO)6 isomer with an Fe–Fe bond and an uncomplexed C=C double bond in the C8H8 ring lying ∼11 kcal mol−1 in energy above trans-(η4,η4-C8H8)Fe2(CO)6 appears to correspond to one of the metastable C8H8Fe2(CO)6 isomers obtained under relatively mild conditions. However, the cis-(η4,η4-C8H8)Fe2(CO)6 structure without an Fe–Fe bond suggested for the other metastable isomer appears to be a high-energy structure with a large imaginary vibrational frequency. Following the corresponding normal mode leads to cis-(η3,η3-C8H8)Fe2(CO)6. For C8H8Fe2(CO)5 the two lowest energy structures are singly bridged cis-C8H8Fe2(CO)4(μ-CO) structures differing only by a 22.5° rotation of the C8H8 ring around the central Fe2 unit. One of these structures is the experimental C8H8Fe2(CO)5 structure. The closeness in energy of these two C8H8Fe2(CO)5 structures is consistent with the experimentally observed fluxionality of this molecule in the NMR spectrum at low temperatures. The unsaturated C8H8Fe2(CO)n (n = 4, 3) structures obtained by further decarbonylation of C8H8Fe2(CO)5 retain the bridging bis(tetrahapto) or bis(pentahapto) C8H8 rings of C8H8Fe2(CO)5 and provide examples of structures with formal Fe=Fe double bonds with the lowest energy such structures having triplet rather than singlet spin states. Viable carbonyl-rich (η2,η2-C8H8)Fe2(CO)8 and (η4,η2-C8H8)Fe2(CO)7 structures represent possible intermediates in the formation of the various C8H8Fe2(CO)n (n = 6, 5) species from cyclooctatetraene and iron carbonyls. [ABSTRACT FROM AUTHOR]

The opposed and parallel structures for the binuclear bis(azulene) 'submarine' sandwiches (C10H8)2M2 (M = Ti, V, Cr, Mn, Fe, Co, Ni) have been optimized using density functional theory. The lowest energy (C10H8)2M2 structures of the early transition metals Ti, V, Cr, and Mn have the azulene units functioning as bis(pentahapto) ligands to each metal atom similar to the azulene ligand in the long-known molybdenum carbonyl complex (η5,η5-C10H8)Mo2(CO)6. The metal-metal bonds in these early transition metal structures have distances and Wiberg bond indices consistent with the formal bond orders required to give each metal atom an 18-electron configuration for the singlet structures and a 17-electron configuration for the triplet structures. For the later transition metals Fe, Co, and Ni, the lowest energy (C10H8)2M2 structures contain pentahapto-trihapto azulene ligands with an uncomplexed CC double bond, similar to that in the long-known iron carbonyl complex (η5,η3-C10H8)Fe2(CO)5. The parallel (η5,η3-C10H8)2M2 (M = Fe, Co, Ni) structures contain metallocene subunits with their metal atoms at long nonbonding distances of 3.5-3.9 Å from the other metal atom, which is located between the azulene C7 rings. Higher energy opposed (C10H8)2Fe2 structures contain an unprecedented distorted η6,η4-azulene ligand using six carbon atoms for bonding to one iron atom as a hexahapto fulvene ligand and the remaining four carbon atoms for bonding to the other iron atom as a tetrahapto diene ligand. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Density functional theory shows that the lowest energy CpMoC3B n−4H n−1 ( n = 8, 9, 10, 11) structures are based on isocloso or similar deltahedra with the molybdenum atom at a degree 6 vertex. Such deltahedra include the capped pentagonal bipyramid for the 8-vertex system. Among such geometries the lowest energy structures have the carbon atoms at the lowest degree vertices (typically degree 4 vertices), no pairs of adjacent carbon atoms (i.e., no C-C edges), and the maximum number of Mo-C edges. Optimizing these factors favoring low-energy CpMoC3B n−4H n−1 ( n = 8, 9, 10, 11) structures leads to a unique lowest energy structure lying more than 10 kcal/mol below the next lowest energy structure for the 8-, 10-, and 11-vertex systems. However, the 9-vertex CpMoC3B5H8 system has three structures within 8 kcal/mol including a structure based on the closo tricapped trigonal prism rather than the isocloso 9-vertex deltahedron. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The experimental realization of pentagonal prismatic structures for M@(M = Co, Fe) containing interstitial transition metal atoms makes of interest the chemistry of corresponding manganese derivatives Mn@. The neutral Mn@Ge10may be regarded as a complex of a polyhedralligand with an interstitial Mn in the +2 oxidation state. However, the lowest energy Mn@Ge10structure with the expected sextet spin state for high-spin d5Mn(II) lies ~23 kcal mol−1in energy above the lowest energy isomer thereby suggesting that such germanium polyhedra function as strong field ligands for encapsulated transition metals. The lowest energy structures for the Mn@anions (z = −1 to −5) are all centered pentagonal prisms. Higher energy Mn@structures have outer Ge10polyhedra based on the tetracapped trigonal prism similar to the lowest energy Co@structure and on the bicapped square antiprism similar to the B10deltahedron. Other Mn@structures have outer Ge10polyhedra with four or five quadrilateral faces as well as six or eight triangular faces, respectively. Bioctahedral (Ge5)2Mn5−structures were also found for the pentaanion with a manganese vertex common to two MnGe5octahedra. The cationic species Mn@was found to have a more complicated potential surface than the anions. Tetracapped trigonal prismatic and bicapped square antiprismatic structures as well as a variety of more open structures were found for Mn@. [ABSTRACT FROM AUTHOR]

Alkali metal salts of the 2-phosphaethynolate anion PCO− synthesized from reactions of CO with NaPH2 or K3P7 have recently become available in quantities for the synthesis of transition metal complexes of the potentially ambidentate PCO ligand (Angew. Chem., Int. Ed., 2013, 38, 10064). This is exemplified by the recently reported rhenium carbonyl complex (triphos)Re(CO)2(PCO) (triphos = MeP(CH2PPh2)3). Density functional theory studies on the related manganese carbonyl complexes Mn(CO)n(PCO) (n = 5, 4, 3) and Mn2(CO)n(PCO)2 (n = 8, 7, 6, 5) are now reported. For the binuclear systems the low-energy Mn2(CO)8(PCO)2 structures are singlet spin state structures having two bridging P-bonded phosphaketenyl μ-PCO ligands without a direct Mn–Mn bond. Carbonyl loss from Mn2(CO)8(μ-PCO)2 is predicted to lead to migration of CO groups from phosphorus to manganese resulting in Mn2(CO)n+2(μ-P2) structures with bridging diphosphido groups as the lowest energy Mn2(CO)n(PCO)2 isomers (n = 7, 6, 5). Isomeric Mn2(CO)6(PCO)2 structures with dihapto bridging η2-μ-PCO ligands at ∼30 kcal mol−1 above the global minimum are also found representing intermediates in the migration of CO groups from phosphorus to manganese. For the mononuclear systems the P-bonded Mn(CO)n(PCO) (n = 5, 4) phosphaketenyl structures are found to lie 20 to 28 kcal mol−1 in energy below the isomeric O-bonded Mn(CO)n(PCO) phosphaethynoxy isomers consistent with previously reported results by Grützmacher and coworkers on R3E(PCO)–R3E(OCP) systems (R = iPr, Ph; E = Si, Sn, Ge, Pb). The lowest energy structure for the tricarbonyl Mn(CO)3(PCO) is a singlet structure with an unusual trihapto η3-PCO ligand. However, higher energy isomeric Mn(CO)3(PCO) structures with P-bonded phosphaketenyl or O-bonded phosphaethynoxy ligands and tetrahedral Mn coordination are also found. [ABSTRACT FROM AUTHOR]

Abstract: The series of cobaltathiaboranes CpCoSB n H n (n =6, 7, 8, 9, 10) related to the experimentally known CpCoSB8H8 and CpCoSB10H10 have been investigated by density functional theory. The lowest energy CpCoSB n H n (n =6–10) structures are the closo deltahedra in accord with expectations for these 2n +2 Wadean skeletal electron systems. In the lowest energy such structures the sulfur atom is located at a lowest degree vertex and the cobalt atom at a highest degree vertex. An alternative bicapped octahedral CpCoSB6H6 structure having the sulfur atom at a degree 3 capping vertex lies only ∼7kcal/mol above the bisdisphenoid global minimum. For the 12-vertex CpCoSB10H10 system the three possible structures based on a B10CoS regular icosahedron lie more than 50kcal/mol in energy below any non-icosahedral structures. The relative energy ordering of ortho

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